Similar proposals by Vale of Glamorgan and Bridgend, and Blaenau Gwent and Torfaen were also thrown out.

But Denbighshire chief executive Mohammed Mehmet said the real reason for rejecting the scheme was partly because the North Wales authorities had asked for help footing the up-front costs.

Mr Mehmet claims the decision is a “missed opportunity” because greater savings would have been made in the medium to longer term to justify the move.

The estimated £14m start-up cost would have been spent on harmonising jobs, pay, council tax, aligning communications and IT services and potential redundancy payouts.

Mr Mehmet’s claims surfaced in letters he sent to a Welsh Government official which were revealed under the Freedom of Information Act.

They show Mr Mehmet reacting critically to Mr Andrews’ decision to turn down three expressions of interest (EoI) in January.

Mr Mehmet said he believed the Minister had rejected the proposals due to costs, and claimed they used the EoI as an “excuse” as they wanted to “reconsider the whole map of local government”.

Documents also revealed Conwy and Denbighshire jointly asked the Welsh Government for financial support and assurances.

They asked for £300,000 in “order to secure the minimum necessary capacity” to develop the merger proposal by June 30 this year.

Mr Mehmet added: “If it was just down to the quality of the EoI they would have told us to do it better.

“Who was going to fund it, this is an enormous amount of money? Who is going to fund the up-front costs, that is the real debate.”

The claims come as documents put before the Assembly’s finance committee earlier this week show Conwy spent £2,500 in preparatory work before the merger was quashed in January. Mr Mehmet said Denbighshire had spent around the same amount.

A Welsh Government spokesperson said: “We appreciate the commitment and effort of those authorities who expressed an interest in proceeding with a voluntary merger.We continue to work with local authorities to make progress on local government reform.

“The First Minister has invited the leaders of all parties to take part in discussions seeking a consensus on a future map for local government. If agreement isn’t possible, we will publish our own map by the summer.”